A phosphor layer of a cathode ray tube (CRT) is where energy of electron beams is charged to photoenergy. As shown in FIG. 1, electrons become luminous by collision with phosphor materials of a phosphor film layer 8 formed on a panel 11 on an opposite side of an observer. The properties of the phosphor layer depend greatly on the properties of the phosphor material that are used.
In general, phosphor materials used in forming the phosphor layer for color picture tubes (CPT) are produced by adding a small amount of impurities that act as an activator to a base body such as zinc sulfides or yttrium oxides, etc., and then allowing the impurities and base body to calcinate for in the range of from about 30 minutes to one hour at a temperature of in the range of from about 700-300.degree. C. Useful activator materials include copper (Cu), gold (Au), rare earth elements, etc.
A process for manufacturing a phosphor film layer for color picture tubes comprises the steps of: coating a photoresist to inside of a panel; exposing the coated panel to light; and developing, graphite coating, etching, and forming graphite stripes to form black matrixes (BM), by photolithography.
A step of forming a phosphor film is followed. A phosphor slurry composition is prepared by suspending phosphor materials in a solution of poly vinyl alcohol (PVA) and ammonium dichromate (ADC) through a slurry method. Referring to FIG. 2, the phosphor slurry composition 22 is coated onto an inside surface of the panel 11 and is circling around the panel through a nozzle 21. The panel is dried by an infrared heater and a shadow mask is deposited onto the coated panel surface to solidify a photosensitive layer thereon by exposing the photosensitive layer by exposure to UV light. The photosensitive layer is developed with water to form a phosphor material pattern.
An aluminum film is formed by coating the phosphor layer between black matrixes inside of the panel, filming to form an organic film, and depositing aluminum. Organic materials remained on the phosphor layer are removed by heat treatment.
As indicated above, a phosphor screen is formed by exposing photosensitive coating layer to UV light, which comprises phosphor materials, polyvinyl alcohol, ammonium dichromate, water and interfacial active agent, etc. However, substantially, photosensitivity mechanism is proceeded by polyvinyl alcohol, ammonium dichromate and water. A mechanism for formation of a phosphor layer is divided into a dark reaction and a light reaction.
A dark reaction means the oxidation-reduction reaction incurring between polyvinyl alcohol and ammonium dichromate in the phosphor material slurry. A light reaction means a reaction in which, after breakage of chains of polyvinyl alcohol, polyvinyl alcohol cross-links by Cr.sup.+3 ions reduced from Cr.sup.+6. Consequentially, in this reaction, solubility of polyvinyl alcohol for water is decreased.
Because water is used in the photoreaction, insufficient water on the coating layer inhibits the reaction, on the contrary, extra water inhibits three-dimensional cross-linking.
Cr.sup.+3 which is produced in the photoreaction and acquired in this reaction again, is reacted with water by competitive reaction to form a stable compound. However, this compound does not attribute to cross-linking. The product can be obtained under the condition that pertinent moisture be maintained on the phosphor layer during the light reaction.
A picture is acquired by illuminating phosphor materials coated onto the interior surface of a panel 11, by energy provided by electron beams fired from an electron gun 14, as shown in FIG. 1. In above the process, the coating process comprises pouring phosphor materials of aqueous solution for coating, exposing to light after precipitating phosphor materials, hardening and washing, sequentially. In the case where the phosphor material is soluble in water, it has drawbacks of not being precipitated and facile to drive off at washing. The phosphor material must not react with water in order to preserve its characteristics. Accordingly, water-soluble phosphor materials have been excluded from consideration even if it has distinguished phosphor efficiency, color coordinates, time of afterglow, etc.